Electric filter



J 6, 9 1.. c. WATERMAN ETAL 3,324,026

ELECTRIC FILTER Filed Jan. 10, 1964 2 l6 /5 Z6 Z2 Z4 25 22a 26a 2Sheets-Sheet 1 INVENTORS.

54 53 a5 LOGAN CZ MTERMAM ALBERT D. Ham/5E 15y THE/E A7'702A/575 HARE/5,MECH, RUSSELL 8: K57? June 6, 1967 L. c. WATERMAN ETAL 3,

ELECTRIC FILTER Filed Jan. 10, 1964 2 Sheets-Sheet 2 HARR/S, K/EcH,RUSSELL & KERN United States Patent I 3,324,026 ELECTRIC FILTER Logan C.Waterman and Albert D. Franse, Houston, Tex., assignors to PetroliteCorporation, Wilmington, Del., a corporation of Delaware Filed Jan. 10,1964, Ser. No. 336,905 13 Claims. (Cl. 204-302) Our invention relates tothe removal of dispersed contaminants from high-resistivity oils thataresubstantially free of dispersed water or that are free of significantamounts of dispersed water by which we have reference to dispersed watercontents so low that they cannot be measured by centrifugal methods.More particularly the invention relates to an electric filter and methodfor removing contaminating dispersed particles, usual-ly solidparticles, from such an oil.

Contaminants in oils give rise to severe problems and various attemptshave been made to remove them by electrical, chemical or mechanicalmeans. Contaminants in lubricating oils induce wear on the surfaces tobe lubricated. Contaminants in fuels tend to clog and erode burnerorifices of critical size. In jet fuels contaminants are particularlytroublesome and are thought to have been the cause of many crashes ofjet aircraft. Contaminants in hydraulic oils tend to clog and/ or erodevalve orifices and pumps or impede the free operation of valve elementsor other elements actuated by the oil.

Such contaminants may enter such oils from different sources or may bepresent as the result of production techniques. Commonly thecontaminants are considered as including siliceous material, e.g. roaddust or atmospheric dust; metallic materials, e.g. particles of metalpicked up from storage or transfer equipment; metallic compounds, suchas rust (iron oxide), etc.; or nonmetallic materials, e.g. particles ofcarbon, filaments of animal or vegetable origin, etc.

The size of such contaminating particles in such oils may vary from lessthan one micron up to 100 microns or more. Conventional filters arecapable of removing most of the particles in the larger portion of thisrange but are either incapable of removing particles less than about 5microns or become quickly clogged therewith or build up pressure dropswhich become impracticably high. It is presently possible by variousknown techniques to count the number of contaminating particles in suchan oil within the range up to 2,000,000 particles/100 ml. of oil,considering particles of a size greater than 1 micron. While there areno fixed standards as to permissible contamination, which of course willdepend upon ultimate use, it is generally desirable that the filtered orpurified oil contain less than 2,000 particles/ 100 ml. of oil and formore highly purified oils less than about 1,000 particles/100 ml. oreven less than 500 particles/100 ml. For example, it is not uncommon tofind jet fuels containing far in excess of 2,000,000 particles/100' ml.and to meet requirements in which purified oil from the filter shallcontain less than .7 mg. per liter of oil.

The present invention is capable of removing substantially all of thecontaminating particles greater than 5 microns in size, usually to avalue of 99.9% or more, and is capable of removing particles less than 5microns in size to a much greater degree than any known mechanicalfilter. It is an object of the invention to provide an electric filterand method capable of such results, but which can also be used whereless exacting results are acceptable. A further object is to provide anelectric filter characterized by low pressure drop,'high throughput andan extraordinary ability to remove extremely small particles, e.g. lessthan 5 microns in size.

It has previously been proposed, e.g. in the patent to 3,324,026Patented June 6, 1967 Hamlin 2,573,967, to remove dirt particles fromcleaning solvent by flowing the solvent through screen electrodes withthe inter-electrode space filled with a loosely packed mass of fibrousmaterial such as glass wool, rock wool or synthetic plastic fibers. Inthe laboratory-type equipment of this patent the flow is parallel to thelines of force and the container is formed of insulating material. Thistype of filter and interelectrode packing is not capable of producingthe results of the present invention. It has also been elsewheresuggested that a mass of open-pore polyurethane foam should fill theinterelectrode space but this alone has not solved the problem.

It is an object of the present invention to provide an improvedelectrode configuration excellently suited to the purification ofcontaminated oils when the interelectrode treating spaces are filledwith suitable porous material. In this respect it is an object of thepresent invention to flow the oil in directions parallel to theelectrodes and transverse to the lines of force of the field.

The present invention is based also on the discovery that new coactionsand unexpected results are obtainable if the interelectrode treatingspaces are narrow and are filled in substantially all sections thereofwith a multielement mass of porous material of high electricalresistivity bridging the electrodes. In the preferred practice of theinvention each interelectrode treating space in each section thereofcontains a multi-element mass comprising at least two thin sheets orlayers of such porous material in face-to-face con-tact, the sheetsextending in each section of the interelectrode treating space as layersparallel to the electrodes and being compressed therebetween with onlysuificient pressure to provide good electrical contact between theelectrodes and the outermost surfaces of the stacked sheets or layers.It is an object of this invention to provide such a multi-layer fillingfor each interelectrode treating space. In other instances themulti-element mass of porous material may be made of chunks of suchporous material in random arrangement in contact with each other, themass bridging the electrodes and being composed of chunks that areindividually porous. It is an object of the invention to employ such amulti-element mass in which the elements are chunks of porous material.

The preferred type of porous material, whether used in layers or chunks,is filamentary polyurethane foam. In making this material polyurethaneis foamed by conventional methods and leached or otherwise processed toproduce passages throughout the mass. The result is a filamentarynetwork, best described as a three-dimensional network of filaments thatare unitary at their junctions. Many of the filaments appear asfilamentary arcs or circles joined unitarily at points of tangency toother filaments. Such filamentary polyurethane foam is commerciallyavailable in different porosities. Use of such filamentary polyurethanefoam in layers or chunks and with flow parallel to the electrodesurfaces and transverse to the lines of force of the field representsthe preferred practice of the invention. It should be understood howeverthat other porous materials can be substituted if used in sheet or chunkform and if less exacting results are acceptable. The same is true of anorientation of filamentary polyurethane foam or other porous materialsarranged in layers or chunks with flow transverse to the layers andelectrodes although the results with such arrangement will ordinarily bedistinctly inferior to the preferred practice of the invention.

It is a further object of the invention to provide a dualflow electricfilter in which the contaminated oil advances in opposite directions inaxially aligned sections of a container.

A further object of the invention is to subject the incomingcontaminated oil to an intense electric discharge, produced byrelatively sharp electrode points, before the 3 oil enters the firstinterelectrode space. Another object is to subject the incomingcontaminated oil to one or more magnetic fields before entry into theinterelectrode spaces to remove at least a part of any particles ofmagnetic material from the oil. Further objects and advantages of theinvention lie in the particular arrangements of stacked, superimposed orconcentric electrodes forming a part of the invention; also in thearrangement of electrodes in a replaceable pack which will permitprecise spacing of the electrodes and easy replacement in an existingcontainer.

Another object of the invention is to provide electrical equipment inwhich contaminated oils flow to-and-fro with respect to the central axisof the container during advancement therealong and in which seals areprovided to prevent any of the oil bypassing the interelectrode spaces.

In the electric filter of the invention the contaminants areelectrically attracted to and deposited on the filaments of theinterelectrode packing material. It is of importance that thesecontaminants remain in such deposited condition throughout the time thatoil is flowing through the filter for purification. It has beendiscovered that this requires maintenance of substantially uniformelectrical conditions and that various deviations therefrom will causethe filter to unload a part of the collected contaminants to augment thecontent thereof in the effluent oil rather than to diminish same. Forexample, unloading will take place upon power failure or a substantialundervoltage applied to the electrodes. Likewise unloading tends tooccur with overcurent, arcing or instantaneous overload conditions or inthe presence of high voltage transients. It is an object of theinvention to divert, bypass, stop or modify the flow of oil through theelectric filter upon occurrence of any such adverse condition.

In this connection the invention preferably includes an efliuent oroutlet valve and a bypass valve in a bypass line interconnecting theefliuent and influent lines of the electric filter. It is an object ofthe invention to divert the effluent of the electric filter, as byclosing the effiuent valve and opening the bypass valve to recycle thefluid, upon power failure or substantial undervoltage applied to theelectrodes or when overcurrent, arcing or instantaneous overload or anyhigh voltage transient occurs.

In the preferred embodiment of the invention we provide an undervoltagerelay producing a signal when the voltage applied to the electrodesdrops below a predetermined value; also an overcurrent relay producing asignal when the current to the electrodes exceeds a predetermined value.It is an object of the invention to close the efiiuent valve and openthe bypass valve upon receipt of either of such signals to prevent fiowof possibly contaminated oil to the outlet line. A further object is toprovide means for periodically testing the electrode current after anovercurrent condition has ocurred to determine when the overcurrentcondition (which normally is only temporary in nature) has cleared up,with normal flow through the system being restored after normaloperating current has been achieved. A particular object of theinvention is to provide for recycling of fluid through the filter duringan overcurrent condition so as to maintain fluid flow therein andfacilitate -reestablishment of normal electrical operating conditionsand to provide a time delay mechanism for maintaining the recycle flow aperiod of time after establishment of normal electrical conditions topermit cleaning up of the effluent oil before coupling same to theoutlet line.

Further objects and advantages of the invention will be apparent tothose skilled in the art from the following description of exemplaryembodiments.

Referring to the drawing:

FIG. 1 is a vertical sectional view of one embodiment of the invention;

FIG. 2 is a transverse sectional view thereof taken along the line 22 ofFIG. 1;

FIG. 3 is an enlarged fragmentary view illustrating layers of porousmaterial between electrodes;

FIG. 4 is an enlarged fragmentary view illustrating chunks of porousmaterial between electrodes;

FIG. 5 is a longitudinal sectional view of an alternative embodiment,while FIGS. 6 and 7 are perspective views of electrode elements thereof;

FIG. 8 is a longitudinal sectional view of a further alternativeconstruction; and

FIG. 9 is a diagram illustrating a preferred arrangement for fluid flowand for the electrical control circuitry.

The electric filter of FIGS. 1 and 2 includes a grounded tubular housinghaving an inner wall 16. The housing 15 is preferably cylindrical butcan be of other cross-sectional shape. It is closed at its ends byremovable heads 18 and 18a held in place by studs 19 and nuts 20. Theinterior of said tubular housing comprises opposed end zones 22 and 22aspaced from each other along the central axis A-A of the housing,opposed treating zones 24 and 24a spaced along said axis inwardly ofsaid end zones and bounded outwardly by the inner wall 16, and a smallcentral zone 25 between the two treating zones.

In the illustrated embodiment the pressured contaminated oil is dividedbetween pipes 26 and 26a respectively opening on the end zones 22 and22a and forming a first pipe means. The two portions of contaminated oilflow toward each other through the respective treating zones 24 and 24ain sinuous or to-and-fro paths, as will be described, to the centralzone 25. The streams here meet and the composite stream dischargesthrough a second pipe means shown as a pipe 27 opening on the centralzone 25.

A central shaft 28 is mounted in cantilever fashion along the axis A-Aby a bushing 30 suitably secured to the head 18 The conductor of ahigh-voltage cable 32 traverses the bushing 30 and is electricallyconnected to the shaft 28. The tubular housing 15 and the heads 18 and18a are preferably grounded.

The shaft 28 carries a plurality of disc-like plate electrodes 35 withintervening spacers 36 comprising a spacing means for spacing the plateelectrodes in each treating zone equally along the axis A--A. A largebarrier 38 formed of insulating material is disposed between thetreating zones 24 and 24a and may provide an inner portion disposedbetween the innermost spaces 36 of the two groups thereof in therespective treating zones. A nut 39 within the end zone 22a is threadedto the shaft 28 to clamp the plate electrodes 35, the barrier 38 and thespacers 36 against the bushing 30 as an assembled unit. Each plateelectrode 35 is peripherally smaller than the inner wall 16 to form anannular passage 40 therebetween.

electrodes 35. Each annular electrode 42 has a centralopening 46 ofsubstantially smaller radius "than the outer periphery of each plateelectrode 35 so that the annular electrodes 42 and the plate electrodes35 overlap to form radial spaces therebetween providing theinterelectrode treating spaces containing the porous material as Will bedescribed. The outer periphery of each annular electrode 42 is slightlysmaller than the inner wall 16 and is sealed thereto by any suitableannular sealing member 48 formed of resilient material such as syntheticrubber or a resilient plastic, these sealing members being in the zonebetween the spacers 44 and the inner wall 16. Such scaling membersprevent any peripheral bypassing of the oil and are important if bestoperating results are to be obtained.

The annular electrodes 42 are electrically connected to the groundedtubular housing 15 through the spacers 44 and the shafts 45. If ahigh-voltage source of unidirectional potential is connected between thetubular housing 15 and the conductor of the cable 32 the annularelectrodes 42 will constitute two sets of grounded electrodes,respectively in the treating zones 24 and 24a, while the plateelectrodes 35 will constitute two sets of live electrodes interspacedwith the grounded electrodes. Electrostatic fields will be establishedin the radial spaces between the live and grounded electrodes so thatsuch fields exist in the interelectrode treating spaces filled with theporous material as will now be described.

Except for the two outermost interelectrode zones 50 and 50a eachsection of each interelectrode treating space that is disposed outwardlyof the central zone 25 is filled with a multi-element mass of porousmaterial of high electrical resistivity bridging the electrodes of theinterelectrode treating space and comprising individual elements of theporous material compressed lightly into contact with each other and withthe electrode surfaces bounding such interelectrode treating space. Inthe embodiment of FIGS. 1 and 2 the individual elements of themulti-element mass comprise at least two thin layers or sheets 54 of theporous material in face-to-facecontact, preferably of annularconfiguration to occupy compositely substantialy the entire volume ofsuch interelectrode treating space. These sheets are preferably made offilamentary polyurethane foam for best results but other porousmaterials in sheet form can be substituted with substantially improvedresults as compared with the same material in block form filling theentire interelectrode space. The electrical and physical properities andfunctioning of such sheets will be later described.

Means may be provided for subjecting the incoming contaminated oil to anelectric blast action tending to impart to the dispersed contaminatingparticles an electric charge just prior to entry into the firstporous-materialfilled interelectrode treating zone. As shown in FIG. 1this is accomplished by a plurality of relatively sharp pointed pins 56extending into each of the outermost interelectrode zones 50 and 50afrom one of the electrodes bounding same in a direction toward the othersuch electrode. These pins are shown as mounted in a circular pattern onthe outermost plate electrodes 35 with their points facing the outermostannular electrode 42 in a circular zone just beyond its central opening46.

If the contaminated oil contains particles of magnetic material thesecan be partially or substantially completely removed by establishingmagnetic fields in the end zones 22 and 22a. The invention oomprehendsany arrangement of permanent magnets in these end zones, exemplified inFIG. 1 as a series of oppositely poled bar magnets 58 mounted in acircular pattern by the heads 18 and 18a in positions extending towardthe outermost annular electrodes 42. Magnetic fields are establishedbetween adja cent bar magnets to attract thereto such magneticparticles. The collected particles can be removed upon disassembly ofthe filter. The pins 56 and the magnets 58 are permissive and need notalways be incorporated in the structure.

The radial intermernber spaces within the central zone 25 may beinterelectrode zones if one of the plate electrodes 35 is substitutedfor the barrier 38. However with the barrier 38 of insulating material,as shown, the space between the innermost annular electrodes 42 of thetwo sets will be equipotential, as will be the radial spaces between thebarrier 38 and each such electrode. Such radial spaces may be filledwith the sheets 54 as previously described, such sheets then actingmerely in a filter capacity, or they may be filled with porous materialhaving better filter characteristics to act as a mechanical filtercollecting some residual contaminants or blocking discharge of a mass ofcontaminants should the system be inadvertently or accidentally operatedto unload the collected contaminants.

With the electric filter shown in FIG. 1 each portion of the incomingstream of contaminated oil enters one of the pipes 26, 26a, flowsinwardly through the magnetic fields between the bar magnets 58 andoutwardly in the first or end interelectrode space 50, 50a to besubjected to the blast discharges from the relatively sharp pointed pins56. Thereafter this portion flows through the annular passage 40 aroundthe end plate electrode 35, radially inwardly through the sheet-filledinterelectrode space, forwardly through the central opening 46 of thenext annular electrodes 42, then outwardly through the next sheet-filledinterelectrode space, and so on. The oil thus moves inwardly andoutwardly toward and away from the central axis AA during its forwardadvancement toward the central zone 25 where it moves outwardly to besubjected to the filtering action of any porous material therein beforedischarging through the pipe 27.

The filter of FIG. 1 can also be employed by reversing the flow in whichevent the total incoming stream will be supplied to the pipe 27 to bedivided by the barrier 38 into portions flowing outwardly through thetwo sets of electrodes in the two treating zones 24, 24a with the sametoand-fro movement relative to the axis AA. In this instance the porousmaterial in the central zone 25 will act as an initial filter and thepointed pins 56 and the bar magnets 58 can be eliminated. The purifiedoil will then flow as two streams from the opposite end zones 22, 22aand can be combined into a single stream passing along an efiluent pipetoa point of storage or use.

As the contaminated oil flows outward or inward through the sheet-filledinterelectrode treating spaces it is subjected to the unidirectionalelectrostatic fields therein. The porous material therein exertssubstantially no mechanical filtering action but forms a network ofbonded filaments on which the contaminants deposit because of the actionof the electric field. This can best be explained by reference to FIG. 3which shows diagrammatically portions of three sheets 54 betweenelectrodes 35 and 42. The stacked sheets 54 fill the interelectrodespace and exist therein in slightly compacted form so that the end facesof the outermost sheets make good electrical contact with the metal ofthe electrodes 35 and 42. The sheets act as voltage dividers and appearto act to some extent as individual electrodes. In this latter respecteach sheet appears to have positive and negative surfaces on oppositesides thereof. Some cantaminants, such as carbon, will deposit on thepositive surface of each sheet while other contaminants, such as ironoxide, will deposit on the negative surface. Siliceous particles, e.g.road dust, may deposit within the interstices of the foam. The existenceof these deposits on such positive and negative surfaces can be provedby analyzing the deposited material on opposite sides of a sheet whenseparated from neighboring sheets.

The incremental voltage drop or gradient measured on a line between anytwo electrodes is not uniform. In this respect, the positive surface ofone sheet is in high-resistive contact with the negative surface of itscont-acting neighbor. The voltage drop across the narrow interfacialcontact zone Z (FIG. 3) of two sheets is higher than the average voltagedrop across each sheet per se even though the thickness of suchinterfacial contact zone is minute compared with the sheet thickness.The result is a much higher voltage gradient in the interfacial contactzone Z, as compared with the voltage gradient in the internal portionsof each sheet or the nominal (aver-age) voltage gradient between theelectrodes calculated by dividing the total applied voltage by thespacing of the electrodes 35 and 42.

The use of stacked sheets or contacting layers filling theinterelectrode treating space has been found to be much superior to theaction when a single body of the same material fills the interelectrodespace as illustrated by the following example employing electric filtershaving 18 pairs of the aforesaid plate and annular electrodes spaced /2inch differing only in that each of the interelectrode treating spacesof filter A contained a single /2 inch layer of filamentary polyurethanefoam while each such treating space of filter B contained four layers ofthe same foam material each /s inch thick. With a unidirectional appliedvoltage of 15 kv. and with oils equally contaminated supplied to eachfilter at the same rate (velocity normal to field being 81 inches/min.)and temperature, all other conditions being the same including time ofresidence in the intense electric fields (18.4 seconds), the number ofresidual particles in the oil after a single pass through filters A andB was not significantly different as to particles in the range of 25-100but was much lower with filter B than with filter A as concerns smallerparticles. In the range of l525,u. the residual particles per 100 cc.were 187 with filter B as compared to 220 with filter A. In the range of5-15 1. the residual particles on this basis were 1,745 for filter B ascompared to 13,200 for filter A. A recycle operation in which the sameoil was recycled through filter B for approximately 30 min. reduced theresiduals in the l5-25u range to 155 and in the 5-15 r range to 785, ascompared to filter A in which such recycle reduced the residuals in the15-25,u range to 215 and in the 5-15 range to 1,360 particles per 100cc. These runs evidence the unexpected superiority of the multi-layerfilter B on a single-pass operation particularly as concerns removal ofcontaminating particles of very small size.

Materials and operating conditions in the multi-layer electric filter ofthe invention are critical to the extent indicated in the followingparagraphs if the highest percentage removal of contaminants is to beachieved. It should be understood however that the materials andoperating conditions herein set forth are capable of modification ifless exacting results are tolerable.

As to the porous material in sheet form, filamentary polyurethane foamis preferred but other junction-bonded filamentary networks made ofglass or synthetic fibers can be employed. Sheets of other porousmaterial of high resistivity, such as mats of randomly arranged or wovenfibers of glass or synthetic fibers if employed in sheet form willproduce results substantially superior to the same uusheeted materialemployed as a single mass filling the interelectrode zones. Syntheticfibers such as polytetarafluoroethylene (Teflon),trifiuorochloroethylene (Kel-F), polyethylene, etc. can thus be employedin matted or junction-bonded form, the fibers being spun of suchmaterials or being shavings thereof.

The porous material should be of high resistivity but will usually havea conductivity, somewhat higher than that of the oil measured in eitherits purified or contaminated state. In this respect the conductivity ofthe porous material will usually be about 5-15 times that of the oil,often in the neighborhood of times the oil conductivity. However thisrelative resistivity is not always a critical factor.

The porosity of the porous material for best results will depend uponthe particular material but will always be such that the material exertssubstantially no mechanical filtering action on the contaminants in theabsence of the electric field. With filters of the invention there willbe virtually no removal of contaminants by the porous material if theelectrodes are not energized. Likewise there will be virtually noremoval of contaminants if the porous material is eliminated and theelectrodes are energized, as compared with the same electrode systemwith the sheets of porous material energized at the same voltage.Filamentary polyurethane foam of various porosity is commerciallyavailable and this material in porosities ranging from about 10-30p.p.i. (pores per inch) will be found quite satisfactory.

The degree of compaction of the layered material in the interelectrodespace is not critical so long as good electrical contact is establishedwith the bounding electrode surfaces. Compaction of the porous materialwill ordinarily be about 10-30%, usually 20-25% for best results whenusing filamentary polyurethane foam. Compaction less than 10% willusually give poor results.

The layers or sheets 54 are desirably quite thin, thicknesses of aboutbeing usually preferred. Likewise the interelectrode treating spaces aredesirably narrow in width, this width ranging from approximately twicethe thickness of the sheets 54 to about 10 times the thickness thereof.Widths of about /2-2" will ordinarily be used and such width willpreferably be in the range of about /4-l%.

The direction of oil flow through the sheets is critical if best resultsare to be obtained. Oil flow in a direction longitudinally of the layersor sheets from end to end thereof is unexpectedly beneficial as comparedwith oil flow in a direction through the sheets perpendicular theretoand parallel to the lines of force, as by using a radial fiow throughperforated electrodes.

Satisfactory purification will be obtainable at various rates of flowthrough the interelectrode spaces, rates of about 10-100"/min. or morecan be used. With a total residence time of 20 seconds in theinterelectrode spaces a purified oil containing about 2,000particles/100 ml. can be obtained at flow rates ranging from about 60-min. A 30-second residence time will produce a purified oil containingin the neighborhood of about 1,200 partieles/ ml. within the same rangeof forward velocities.

Nominal or average gradients may vary over a relatively wide range butare relatively high as compared with gradients employed in electricemulsion treaters. The nominal gradient will normally exceed 20 kv./in.and best results will usually be obtained in the range of about 30-60kv./in. or higher. This is true over a wide range of conductivities ofthe oil but the desirable gradients will usually be higher with oils ofhigher resistivity. For example an oil of a specific resistance(ohm-cm.) of 1X10 containing a large amount of contaminants was reducedto 900 particles/100 ml. at a gradient of 30 kv./in. while a similar oilof a specific resistance of 17 l0 contained 1,000 particles/100 ml. ofcontaminants when treated at 50 kv./in.

Avoidance of bypassing at the peripheries of the annular electrodes 42is important for best results. For example, if the metal electrodes forma snug sliding fit with the inner wall 16 without the sealing members 48the effluent particle count will be double or more as compared withelimination of such bypassing. It is not uncommon to be able to reducethe efiluent particle count from about 2,000 to about 1,000 per 100 ml.of oil merely by eliminating the minute bypassing which takes placebetween snug-fitting electrode peripheries and the inner wall 16.

Some types of contaminants are more easily removed from the oil by thefilter than others. Among those commonly found in fuels or hydraulicoils iron oxide is the most difficult to remove, followed by siliceousparticles such as road dust and by filamentary contaminants such asfibers of animal or vegetable origin. Under the same conditions, an oilcontaminated with iron oxide alone was found to have an effluentparticle count of about 1,450 particles/100 ml. When the contaminant wasroad dust present in the same amount the particle count was about 820/100 ml. and when the contaminant was a mixture composed largely ofminute filamentary material the count was about 335 particles/100 ml. Onthe other hand a mixture of the above contaminants, similarly treated,give a particle count of about 966 parts/100 ml., evidencing that amixture of contaminants is more readily purified than some of thecontaminants alone.

The multi-layer porous-material filling for the interelectrode treatingspaces has a relatively long useful life but this life will of coursedepend upon the degree of contamination of the oil being purified. Ithas been found that filamentary polyurethane foam remains excellentlyeffective until loaded with solids to the extent of about 2% or more ofthe Weight of the foam. The particle content of the efiluent oilincreases gradually with progressively greater loadings of the foam upto a loading of about 10% of solids but above this the residual particlecount and the electrical load increase rapidly. The above is withonce-through treatment. If the contaminated oil is recirculated throughthe treating zone a count of less than 2,000 particle-s/ 100 ml. can beobtained even with loadings up to 10% by weight of the foam.

When the porous material in the interelectrode spaces becomes loaded tosuch an extent that continued operation becomes unsatisfactory on aonce-through or recirculation basis it is best to replace the porousmaterial rather than to attempt to remove the collected contaminants.About 10% or more of the collected solids can be washed from the porousmaterial by turning off the voltage and continuing the oil flow.Vibration of the porous material will remove a portion of the collectedmaterial as will reversal of the polarity applied to the electrodes.

The temperature of the contaminated oil is not critical and the electricfilters of the invention remain operative over a wide temperature range.Commonly the oil will be at or near atmospheric temperature but oils ofa temperature of about -100250 F. or beyond can be purifiedsatisfactorily.

There is very little pressure drop on the oil during flow through theelectric filters of the invention. This pressure drop is ordinarilysubstantially less than 10 psi. and commonly much less. The pressuredrop is reduced even more if a double-flow filter of the type shown inFIG. 1 is employed. Also such double-flow filter makes possible the useof closer electrode spacings for the same eifectiveness of particleremoval.

The invention may be incorporated in various other embodiments. FIG. forexample illustrates an embodiment in which the housing or casing isformed by a flanged housing 60 to which flanged heads 61 and 62 arebolted, these heads respectively having outlet and inlet pipes 63 and 64attached thereto. The electrode unit is encapsulated and easily replacedby merely removing one of the heads. This electrode unit comprises aplurality of annular electrodes 65 with central openings 66, see FIG. 6,held apart by spacing members 67 stacked one above the other. Annularelectrodes 65 are disposed there- 'between and centered by shoulders atone or both ends of each spacing member. Each spacing member also has anintermediate shoulder 69 on which rests the peripheral edge of a plateelectrode 70 having a ring of openings 71 near the periphery, see FIG.7, corresponding to the annular passages 40 of the embodiment of FIG. 1.Each interelectrode treating space is filled with stacked sheets 72 aspreviously described.

Each plate electrode 70 may carry an attached contact spring 74 at itscenter, each such contact spring depending through the central opening66 of the annular electrode 65 therebelow and pressurally contacting thenext lower plate electrode 70. With this arrangement the electrodeassembly can be stacked progressively at the point of manufacture, thespring contacts serving to electrically connect the plate electrodes 70.Alternatively both ends of each spring contact may be welded orotherwise attached to the plate electrodes during assembly. Thelowermost depending contact spring may hang free and depend into thespace provided by the head 62 to create an electric blast from its lowerend, acting to charge dispersed particles in the oil entering throughthe pipe 64. This oil advances longitudinally of the housing 60 with ato-and-fro motion as indicated by the arrows. The required high-voltageunidirectional potential may be delivered to the top plate electrode 70by a spring contact 75 permanently fixed to a bushing 76 which conductsthe high-voltage lead to the interior of the vessel.

The entire structure may be rigidified by encapsulation within a sheath77 with the encapsulating material extending inward at the ends to holdthe end annular electrodes 65 in place. Most desirably the encapsulatingsheath 77 may be molded in place in the flanged housing 60 so that thehousing and electrode assembly can be replaced as a unit when the porousmaterial becomes contaminated. Alternatively the encapsulating sheath 77and its electrode assembly can be replaced by making the sheath asliding fit within the flanged housing 60.

FIG. 8 illustrates another embodiment in which sheets or layers ofporous material 79 are stacked side-by-side in each section of eachinterelectrode treating space between concentric or planar electrodes 80and 82 corresponding generally to the electrodes 35 and 42 of FIG. 1 orthe electrodes 70 and 65 of FIG. 5. The electrodes 80 are electricallyconnected and supported by a framework 83 which in turn is supported byinsulators 84. These electrodes are energized by a high-voltage leadextending through a bushing 85. The electrodes 82 are electricallyconnected by a framework 86 grounded to the housing 87. In thisembodiment the interelectrode spaces are not radial but it will beobserved that the flow of contaminated oil is longitudinally of thesheets 79 of porous material, parallel to the electrodes and transverseto the lines of force of the field.

In each of the embodiments thus far described the porous materialfilling the interelectrode treating spaces is in sheet form. It ispossible in some instances to substitute chunks of the same porousmaterial as suggested in FIG. 4 to form the multi-element mass. Thechunks 90 there shown are compressed lightly between oppositelypoledelectrodes 91 and 92. It is essential that each chunk be of highlyporous material, preferably one of the filamentary materials previouslydescribed. The degree of compaction is similar to that previouslydescribed, being sufficient to maintain good electrical contact with theelectrode surfaces and to form zones of interfacial con tact between thechunks. Here the zones of interfacial contact will be randomly arrangedand not continuous or irregularly continuous along the length of theinterelectrode space. The porous material of each chunk is readilycompressible, causing adjacent chunks to conform and contact oversubstantially their entire surfaces. As a result the oil does not flowthrough pores between the chunks but rather is confined to flow throughthe pores of the chunks themselves while being acted upon byelectrostatic stress. The chunks here act as voltage dividers insomewhat the same manner as in the previously described embodiments. Thesize of the chunks is not critical but there is some preference forchunks of irregular shape, e.g. chunks torn or chopped from a sheet orblock of material and of an average size from about /s up to about A" ormore with electrode spacings within the range previously described, thelarger chunks being employed with larger electrode spacings.

Referring to FIG. 9, a filter 95, which may be any of the filterspreviously described, has a fluid inlet 96 and a fluid outlet 97, with ahigh voltage line 98 entering through an insulating bushing 99. A pump101 is positioned in the inlet line and is driven by a pump motor 102energized from a separate power source 102a under the control of amagnetic switch shown. A valve 103 is positioned in the outlet line forcontrolling flow of fluid from the filter. Another valve 104 isconnected in a bypass line 105 which provides for fluid flow from thefilter outlet back to the filter inlet. It is preferred to have thevalve 103 normally closed and moved to the open position by a valvesolenoid 106. Similarly it is preferred to have the valve 104 normallyopen and move to the closed position by a valve solenoid 107. Then inthe event of any electrical power failure to the valves, possiblycontaminated oil from the filter would be diverted from the outlet lineand, in the embodiment shown herein, recycled through the filter.

The high voltage supply for the filter is indicated generally at and maybe conventional in design. A 110 volt 60 cycles per second power sourcemay be connected through the power winding of a saturable core reactor111 to the primary winding of a voltage step-up transformer 112. Thesecondary winding of the transformer 112 is connected to a rectifier 113with one terminal, usually the positive terminal, of the rectifierconnected to the high voltage line 98 and with the other terminal of therectifier connected through a milliammeter 114 and a variable resistor115 to circuit ground. A voltage divider comprising resistors 116, 117may be connected across the rectifier output with a kilovoltmeter 118coupled across the resistor 117. A DC. current source 119 is connectedto the control winding of the saturable core reactor 111 providing meansfor controlling the output of the rectifier by varying the impedancedrop across the power winding of the reactor. A typical filter mayoperate at about 18,000 volts D.C. at 1.5 milliamperes current.

The control circuitry preferably includes an undervoltage sensing deviceand an overcurrent sensing device. Short duration overcurrent conditionsmay occur from time to time in the operation of electric filters and itis preferable to maintain the filter in operation as this normallyprovides the best means for terminating the overcurrent condition.However, during the existence of an overcurrent, the effluent from thefilter may contain contaminants in excess of that normally in theeffiuent. The control circuitry includes means for diverting filterefiluent from the outlet line during and for a period of time after theexistence of overcurrent in the filter. The control circuitry alsoincludes means for periodically checking the current after detection ofan overcurrent for the purpose of restoring the filter flow pattern asearly as practicable after restoration of normal current in the filter.

The overcurrent detecting device is indicated at 125 and may comprise athyratron tube 126 and a relay K1. The control grid and cathode of thethyratron 126 are connected across the resistor 115 and the plate isconnected to the positive terminal of a DC power source 127. Thenegative terminal of the power source is connected through the coil ofthe relay K1 and through a normally closed contact set 128 of a relay K3to circuit ground. The resistor 115 is adjusted so that the voltagedeveloped thereacross by the electrode current will fire the thyratroninto conduction when the electrode circuit current exceeds apredetermined value. Conduction in the thyratron actuates the relay K1to open the normally closed contact set 129 and close the normally opencontact set 130.

The undervoltage responsive device is indicated at 133 and may comprisea relay K4 having its coil connected in parallel with the primary of thetransformer 112. Relay K4 will be actuated when the voltage at theprimary of the step-up transformer reaches a preset value and will dropout when the primary voltage falls below a preset value. Hence undernormal operation, the relay K4 is actuated and its contact set 134 isclosed, connecting power to the coil of relay K5.

The relay K5 has a contact set 135 connected in the control circuit forthe pump motor 102 and another contact set 136 connected in the controlcircuit for the valve solenoids 106, 107. The relay K5 permits operationof the pump motor 102 and also permits actuation of the valves to directthe filter effluent to the outlet line only when both voltage andcurrent conditions are within prescribed limits, thereby functioning asan and or combination control device. These actions are effected asfollows.

With normal operating voltage applied to the system, undervoltage relayK4 is energized to close contact set 134 which in turn energizes relayK5 closing contact sets 135 and 136. Closing of contact set 135energizes the pump motor 102 from its separate power source 102a to pumpfluid through the filter. When contact set 136 is closed, power iscoupled through it and the contact set 129 to the coil of a relay K6which functions as a recycle time delay device. Under the circumstancesjust described, power is also coupled through contact set 129 andcontact set 136 to contact set 137 of relay K6 and thence to solenoids106 and 107 to move valve 103 to the open condition and valve 104 to theclosed condition. This is the normal operating condition of the system.

If the voltage across the primary of transformer 112 falls below thepredetermined value, relay K4 is de-energized, relay K5 is de-energized,relay K6 is de-energized, valve solenoids 106 and 107 are de-energized,and pump motor 102 is de-energized. When the voltage across thetransformer primary increases to the predetermined value, relay K4 isenergized, relay K5 is energized, relay K6 is energized, and pump motor102 is energized. Relay K6 incorporates a time delay mechanism whichdelays the closing of contact set 137 a predetermined period of timeafter closing of contact sets and 136. Typically this may be in theorder of two to four minutes. This delay permits the establishment offluid flow through the filter and the recirculating or recycling orfiltered fluid one or more times through the filter so that normalfiltering operation can be established to bring the efiluent to itsnormally purified condition. After passage of the predetermined time,contact set 137 is closed and valves 103, 104 are actuated to direct thefilter effluent to the outlet line.

The control system includes means for periodically testing the existingcurrent in the electrode circuit after actuation of the overcurrentdevice to determine if the overcurrent condition has been cured. In thepreferred embodiment disclosed herein, this periodic checking isaccomplished by a reset and test device 140 which periodically resetsthe overcurrent device, permitting the overcurrent device to be againactuated if the overcurrent condition still exists. This resetting andtesting operation is carried out within the time delay period of therecycle time delay relay K6 so that the bypass fluid fiow pattern is notdisturbed. Then if normal current conditions exist, the bypass fluidflow path will be restored to the normal flow pattern by closing ofcontact set 137. If normal current conditions do not exist at the timeof resetting and testing, the relay K6 will be de-energized before itstime delay period has expired.

The reset and test device 140 includes a relay or switch K2 and anotherrelay or switch K3. The coil of the relay K2 is energized from the powersource through contact set 130 of relay K1 when relay K1 is actuated byan overcurrent condition. Relay K2 includes a time delay element whichdelays closing of the contact set a predetermined period after closingof contact set 130. Typically this delay may be about sixty seconds andshould always be less than the delay in closing of contact set 137 ofrelay K6. Closing of contact set 150 energizes the coil of relay K3through a DC. power source 151. Actuation of relay K3 opens contact set128 and thereby opens the plate circuit of the thyratron 126 andde-energizes the coil of relay K1.

De-energization of relay K1 opens contact set 130 which in turn openscontact set 150 and de-energizes relay K3. A resistor 152 and capacitor153 are connected in parallel with the coil of relay K3 to provide ashort time delay in the de-energization of relay K3 before contact set128 is closed. This short time delay permits the thyratron tube tode-ionize after removal of the plate potential.

If the overcurrent condition no longer exists, the thyratron 126 willremain extinguished and the contact set 129 will remain closed,permitting the relay K6 to complete its time delay, close contact set137 and actuate both valves. If however the overcurrent condition stillexists, closing of contact set 128 will apply potential to the plate ofthe thyratron and it will be triggered into conduction by the high gridpotential developed across the resistor 115. Conduction of the thyratronwill open contact set 129 and de-energize relay K6 before the time delayperiod thereof expires, thus maintaining the bypass fluid flow patternestablished on initial detection of the overcurrent condition.Conduction in the thyratron will 13 result in closing of contact set 130and the initiation of another reset and test cycle as previouslydescribed. The reset and test cycle will continue periodically until theovercurrent condition has terminated.

Manual override switches may be interposed in the system to change theautomatic operation described above and permit manual control. Thusmanual closing of an override switch 160 in the control circuit of themotor 102 will permit starting the pump 101 at any time. Manual closingof an override switch 161 in the control circuits of the valves 104 and106 will shift the system from bypass to on-stream operation. Manualoverride switches can be provided at other or alternative positions topermit manual control of the system.

The control circuitry of FIG. 9 and the control of actions therebyeflected are useful with various electric filters or treatersirrespective of the material bridging the electrodes and the arrangementthereof in multiple layers. Such a control insures that the effluentdelivered to other equipment will be above set specifications.

Various changes and modifications can be made in the above-exemplifiedapparatus and methods without departing from the spirit of the inventionas defined in the appended claims.

We claim:

1. An electric filter for removing suspended contaminants fromhigh-resistivity oils free of significant amounts of dispersed water,said electric filter including in combination:

a pair of spaced parallel electrodes providing an interelectrodetreating space therebetween;

a multi-element mass of porous material of high electrical resistivityfilling all sections of the interelectrode treating space and bridgingsaid electrodes, 'said rnulti-element mass comprising deformableindividual elements of said porous material compressed together in eachsection of said interelectrode treating space sufliciently to blocksignificant fluid flow between the elements, whereby fluid flow takesplace substantially exclusively through the pores of said elements;

means for electrically insulating said electrodes from each other andfor establishing a high-gradient unidirectional electric field in saidinterelectrode treating space; and

means for flowing the contaminated oil through the pores of saidelements.

2. An electric filter as defined in claim 1 including a housingsurrounding said electrodes providing an entrance zone for thecontaminated oil opening on one end of said interelectrode treatingspace, a plurality of relatively sharp pointed pins in said entrancezone electrically connected to one of said electrodes, and a member ofopposite polarity toward which said pointed pins face but spacedtherefrom to establish electric blasts from said pins toward saidmember, said electric blasts acting on said contaminated oil before itspassage through said pores of said elements.

3. An electric filter as defined in claim 1 including a housingsurrounding said electrode-s providing an entrance zone for thecontaminated oil opening on one end of said interelectrode treatingspace, and means for establishing magnetic fields in said entrance zoneacting on said contaminated oil before its passage through said pores ofsaid elements.

4. An electric filter as defined in claim 1 in which said interelectrodetreating space is of a length much greater than its width, and includinga housing surrounding said electrodes providing entrance and exit zonesrespectively communicating with opposite ends of said interelectrodetreating space, said flow means including an influent pipe meansdelivering the contaminated oil to said entrance zone and an eflluentpipe means conducting the purified oil from said exit zone, said oilflowing lengthwise of said interelectrode treating space transverse to14 the lines of force of said field and through the pores of saidelements. 1

5. An electric filter as defined in claim 1 in which said individualelements of the multi-element mass in each section of the interelectrodetreating space comp-rise at least two thin sheets of said porousmaterial disposed side by side in face-to-face contact extendingparallel to the electrodes bounding said interelectrode treating spaceand compressed lightly together therebetween.

6. An electric filter as defined in claim 5 in which said thin sheetsare formed of filamentary polyurethane foam.

7. An electric filter as defined in claim 6 in which said flow meansincludes means for flowing the contaminated oil in a direction parallelto said electrodes and longitudinally of said sheets of filamentarypolyurethane foam.

8. An electric filter as defined in claim 1 in which said porousmaterial is an easily deformable material, and in which said individualelements of said multi-element mass are chunks of such deformable porousmaterial in random arrangement and in contact with each other fillingsaid interelectrode treating space, said chunks being compressedtogether to deform the contacting chunks sufficiently to substantiallyclose any spaces therebetween and thus compel said oil to flow throughthe pores of such deformed chunks, such compression being sufficient toforce the chunks at the boundaries of said mass into electrical contactwith the elect-rode surfaces bounding such interelectrode treatingspace.

9. An electric filter as defined in claim 8 in which said chunks ofdeformable porous material are chunks of filamentary polyurethane foam.

10. An electric filter for removing suspended contaminants fromhigh-resistivity oils free of significant amounts of dispersed water,said electric filter including in combination:

sets of closely spaced electrodes providing interelectrode treatingspaces each of a width of about V2-2 and of a length several times suchwidth;

a plurality of thin sheets of porous material of high resistivityextending lengthwise of each interelectrode treating space in eachsection thereof lightly compacted together therein between the electrodesurfaces thereof with the outermost surfaces of the outermost sheets inelectrical contact with said electrode surfaces, each of said sheetsbeing of a thickness of about /s%", each sheet having a porosity ofabout 10-30 pores per inch, the degree of compaction of the porousmaterial being about l0-30%;

means for insulating said electrode sets from each other and forestablishing high-gradient unidirectional electric fields in saidinterelectrode treating spaces; and

means for flowing the contaminated oil lengthwise of said interelectrodetreating spaces and said sheets of porous material therein to flowtransverse to the lines of force of said electric fields.

11. An electric filter for removing suspended contaminants fromhigh-resistivity oils free of significant amounts of dispersed water,said electric filter including in combination:

a grounded tubular housing having an inner wall;

a plurality of annular electrodes within and spaced along said housingin parallel relation, said annular electrodes having peripheriesadjacent said inner wall, each annular electrode having a centralopening;

sealing means including sealing members at the peripheries of saidannular electrodes sealing same in fluid-tight relation with said innerwall;

means for electrically connecting said annular electrodes together andto said housing, said annular electrodes forming a grounded set ofelectrodes;

a plurality of plate electrodes respectively between said annularelectrodes having peripheries larger than said central openings thereofbut smaller than said inner wall to form annular passages between suchinner wall and such peripheries;

means for electrically connecting said plate electrodes together andinsulating same from said housing, said plate electrodes forming anenergized set of electrodes, there being an annular interelectrodetreating space between each pair of opposed electrodes of said setshaving inner and outer ends respectively communicating with the centralopening and the annular passage of the electrodes bounding suchinterelectrode treating space;

a source of unidirectional potential connected between said electrodesets to establish electric fields in said interelectrode treatingspaces;

a mass of porous material of high electrical resistivity filling each ofsaid interelectrode treating spaces and in contact with the plate andannular electrodes bounding same; and

means for flowing said high-resistivity oil successively through saidinterelectrode treating spaces and thus through the masses of porousmaterial therein, such oil moving toward and away from said central axisin its successive flow through said interelectrode treating spaces, saidcentral openings and said annular passages.

12. An electric filter as defined in claim 11 in which said housingprovides an entrance zone communicating with a first of saidinterelectrode treating spaces, said means for flowing saidhigh-resistivity oil successively through said interelectrode treatingspaces including a pipe delivering such oil to said entrance zone, therebeing a plurality of relatively sharp pointed pins in said entrance zoneelectrically connected to one of said electrodes, and a member ofopposite polarity toward which said pointed pins face but spacedtherefrom to establish electric blasts from said pins toward saidmember, said electric blasts acting on said oil before its passagethrough said first interelectrode treating space.

13. An electric filter for removing suspended contaminants fromhigh-resistivity oils, said electric filter including in combination:

a tubular housing having a central axis, opposed end zones spaced alongsaid axis, an inner wall extending between said end zones, opposedtreating zones spaced along said axis inwardly of said end zones andbounded outwardly by said inner wall, and a central zone between saidtreating zones;

a first pipe means comprising two pipes respectively communicating withsaid end zones;

a second pipe means communicating with said central zone;

means for flowing portions of said contaminated oil in oppositedirections respectively through said treating zones, said last-namedmeans including means for delivering said contaminated oil to one ofsaid pipe means to advance toward the other of said pipe means and meansfor withdrawing purified oil from the latter;

means for diverting each of said oppositely-flowing oil portions to flowsuccessively toward and away from said central axis during flow throughthe respective treating zones, said diverging means including aplurality of parallel electrically-connected annular electrodes spacedfrom each other along said axis forming a grounded set of electrodes,each annular electrode having a central opening, a plurality of plateelectrodes respectively between said parallel annular electrodes andhaving outer peripheries spaced from said inner wall, and meansextending from plate electrode to plate electrode through said centralopenings of said annular electrodes electrically connecting said plateelectrodes together to form an energized set of electrodes electricallyinsulated from said grounded set of electrodes, there being annularinterelectrode terating spaces between said annular electrodes and saidplate electrodes;

masses of porous material filling said interelectrode treating spaces;and

means for establishing a unidirectional potential difference betweensaid sets of electrodes to establish electrostatic fields in saidinterelectrode treating spaces. 1

References Cited UNITED STATES PATENTS 531,183 12/1894 Harris 204--302661,189 11/1900 Olsen et al. 2l0336 1,293,114 4/1919 Kendrick 2104962,534,907 12/1950 Ham et al 204-188 2,573,967 11/1951 Hamlin 204-3023,190,827 6/1965 Kok et al. 204-186 3,252,885 5/1966 Griswold 204302JOHN H. MACK, Primary Examiner.

HOWARD S. WILLIAMS, Examiner.

T. TUFARIELLO, Assistant Examiner.

1. AN ELECTRICE FILTER FOR REMOVING SUSPENDED CONTAMINANTS FROMHIGH-RESISTIVITY OILS FREE OF SIGNIFICANT AMOUNTS OF DISPERSED WATER,SAID ELECTRIC FILTER INCLUDING IN COMBINATION: A PAIR OF SPACED PARALLELELECTRODES PROVIDING AN INTERELECTRODE TREATING SPACE THEREBETWEEN; AMULTI-ELEMENT MASS OR POROUS MATERIAL OF HIGH ELECTRICAL RESISTIVITYFILLING ALL SECTION OF THE INTERELECTRODE TREATING SPACE AND BRIDGINGSAID ELECTRODES, SAID MULTI-ELEMENT MASS COMPRISING DEFORMABLEINDIVIDUAL ELEMENTS OF SAID POROUS MATERIAL COMPRESSED TOGETHER IN EACHSECTION OF SAID INTERLECTRODE TREATING SPACE SUFFICIENTLY TO BLOCKSIGNIFICANT FLUID FLOW BETWEEN THE ELEMENTS, WHEREBY FLUID FLOW TAKESPLACE SUBSTANTIALLY EXCLUSIVELY THROUGH THE PORES OF SAID ELEMENTS;MEANS FOR ELECTICALLY INSULATING SAID ELECTRODES FROM EACH OTHER AND FORESTABLISHING A HIGH-GRADIENT UNIDIRECTIONAL ELECTRIC FIELD IN SAIDINTERELECTRODE TREATING SPACE; AND MEANS FOR FLOWING THE CONTAMINATEDOIL THROUGH THE PORES OF SAID ELEMENTS.